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BillionMail webmail (Roundcube) not working: login, connection and sending errors

BillionMail includes Roundcube, a webmail where you read and answer mail for your mailboxes (support@, hello@ and so on). This guide covers the problems people hit most: the page won't open, login fails, mail won't send, or new mail never shows up.

Where is webmail?

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https://your-mail-host/roundcube/

If your BillionMail uses a custom HTTPS port, include it:

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https://your-mail-host:PORT/roundcube/

.

Problem 1: "Login failed"

• Use the full email address as the username, e.g.
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  [email protected]
  , not just "support".
  
• Use the mailbox password, not your BillionMail admin password. They're different.
  
• Not sure of the password? In BillionMail, open Mailboxes, edit the mailbox and set a new one.
  
• Still failing? The login check is done by the Dovecot container. See Problem 2.
  

Problem 2: "Connection to storage server failed"
Roundcube can't reach Dovecot, the part that stores mail. Open Settings > Service in BillionMail and check that every service (postfix, dovecot, webmail, rspamd, pgsql, redis) says Running. Click Restart next to dovecot and then webmail.


From the command line, first list your container names:

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docker ps --format "{{.Names}}" | grep -i billionmail

You'll see names like

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billionmail_xxxx-dovecot-billionmail-1

. Use yours in place of DOVECOT and WEBMAIL:

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docker restart DOVECOT WEBMAIL docker logs --tail 50 DOVECOT

Errors about certificates or "Permission denied" in that log point to the real cause.

Problem 3: "SMTP Error (535): Authentication failed" when sending
Reading works, sending doesn't. Roundcube hands outgoing mail to Postfix, which checks the password with Dovecot.

• Log out of webmail and in again (an old session can keep an old password).
  
• Restart postfix and dovecot in Settings > Service.
  
• Check the mail log from your BillionMail folder (
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  /www/dk_project/dk_app/billionmail/billionmail_XXXX
  on aaPanel):
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  tail -n 50 logs/postfix/mail.log

Problem 4: Blank page, 502 or 504 error
The webmail container (Roundcube runs on PHP-FPM) isn't answering. Restart webmail in Settings > Service, wait 20 seconds and reload. If it comes back, check its log:

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docker logs --tail 50 WEBMAIL

A full disk also causes this. Check with

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df -h

.

Problem 5: You can log in, but new mail never arrives
Sending and receiving are separate. For receiving, the internet must find and reach your server:

• MX record:
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  dig +short MX news.example.com
  must show your mail host.
  
• Incoming port 25: from another computer,
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  nc -vz -w 5 your-mail-host 25
  must connect. Open port 25 in aaPanel's Security page and your provider's firewall.
  
• Cloudflare: the mail host record must be DNS only (grey cloud).
  

Send a test from a Gmail account. If Gmail returns a bounce message, it tells you exactly why.

Using a mail app instead (Outlook, Thunderbird, phone)
The Copy link under "Login info" on the Mailboxes page gives you the settings. Usually:

• Incoming (IMAP): your mail host, port 993, SSL/TLS
  
• Outgoing (SMTP): your mail host, port 465 (SSL/TLS) or 587 (STARTTLS), login required
  
• Username: the full email address
  

Open ports 993, 465 and 587 in aaPanel's Security page. A certificate warning in the app means you haven't applied a Let's Encrypt certificate yet; see BillionMail SSL and hostname fix.

Sources: BillionMail on GitHub · Roundcube wiki


More BillionMail troubleshooting

• Port 25 blocked: emails not sending
  
• SSL certificate won't apply
  
• DKIM fails although the record exists
  
• Emails stuck in the send queue
  
• Can't open the dashboard
  
• Emails going to spam
  
• Update safely and roll back
  

Applies to BillionMail 4.9 installed through aaPanel or the install script, October 2026.